Skin pigmentation and thickening of the upper layer of the skin called the corneum are the body's natural protective reactions to exposure to shortwave ultraviolet energy produced by the sun; these reactions are the skin's defense against further assault.
Skin pigmentation, or tanning, is the result of a complex biological process, and to understand it, one most understand the skin's response to different wavelengths of ultraviolet radiation.
Deep down in the skin are special cells called melanocytes. Once these are stimulated with ultraviolet light, they will utilize substances which they have stored up to produce the pigment melanin. Because these substances only absorb shortwave (UVB) ultraviolet light, these UVB rays must be present in order to achieve melanin production. Longer wavelength ultraviolet (UVA) can also formulate melanin but only when there exists enough sensitizing material in the skin to bring about a UVB-type reaction. However, this requires a very high radiation UVA intensity for a long period of time. On the other hand, UVB can induce the same desired melanin production utilizing very low levels of radiation with more frequent exposures.
The pale pink colored melanin granules formed in the melanocytes will travel upward toward the horny layer or corneum. They are stored around the nuclei of the keratin cells there. In this manner, the pigment protects the UVB sensitive DNA located inside the nuclei without impeding the other positive effects of ultraviolet light.
In the preliminary stages of melanin production, very little protection is offered to the skin. In order to render the pigmentation process effective, the melanin granules must darken (oxidize). This requires a higher dosage of longer wave UVA.
The dosage of UVA must be sufficiently high in order to provide enough energy to initiate the oxidation process. It must be remembered that UVA rays are not as energetic as UVB rays. Longwave radiation is essential because high doses of shortware rays will activate substances in the body such as absorbic acid and cysteine which hinder the tanning process. These antioxidants not only inhibit oxidation of pigment but can even reverse the process.
Thus, UVB serves to synthesize the pigment granules while UVA ensure their oxidation. Together they form a light protection mechanism.
UVB is also essential in developing the skin callosity in the horny layer or corneum. This light-induced thickening stabilizes the skin to guarantee protection from excessive radiation. After the skin has been exposed several times, this callosity will develop within one to three weeks and can remain for several months.
Most tanning lamps produce a spectrum of ultraviolet light which is similar to that of the sun. Most lamps provide the small amount of UVB necessary to initiate the tanning process while at the same time, providing the UVA needed to darken the pigment (melanin).
Ultraviolet tanning lamps and tanning equipment used in the United States must comply with very specific regulations which are enforced by an agency of the Food and Drug Administration. These regulations restrict certain ultraviolet lamp characteristics and require extensive labeling of lamps and suntan equipment.
The U.S. FDA defines UVA as the region of 320 nanometers (nm) - 400 nm and UVB as the region of 260 nm-320 nm.
In the design of suntanning equipment and UV sources it is necessary to consider that tanning ability and tanning characteristics vary from one individual to another. In this regard there are two main factors which should be considered:
1. Skin Type--this refers to the (genetic) capability of an individual to produce and maintain a pigmentation in the skin. It is determined by the histologic response of the skin to ultraviolet radiation and classified by the observable effects.
2. Present Skin Pigmentation--this refers to the relative Pigmentation level of the skin at the time just prior to UV exposure. Previously well-tanned skin, exhibiting a high level of pigmentation is generally more resistant to erythema (sunburn) and hence may tolerate higher levels of UVB before the onset of Minimum Perceptible Erythema (MPE). Increased UVB will elicit, however, an increased melonogenic effect ultimately leading to a darker appearing skin. Previously, untanned skin will be more susceptible to UVB induced erythema and therefore UVB levels should be minimized in the early portion of an indoor tanning program.
Because of the factors mentioned above it is necessary in a commercial indoor tanning application or in the consumer tanning products marketplace to offer sunlamp products which are appropriate to the range of "tannable" skin types and skin conditions. This means that sunlamp product manufacturers, to be fully competitive, must offer products which produce the radiative characteristics necessary for safe and effective tanning of a range of skin types and conditions. To this end many manufacturers offer a variety of ultraviolet sources which when used in conjunction with their tanning equipment give the desired ranges of UVA and UVB appropriate for the person(s) undergoing the tanning process.
To cover the range of ultraviolet lamps to meet the needs of the market, equipment manufacturers and distributors generally make available three separate groups of lamps having the following characteristics: 1. Lamps with a relatively low proportion of UVB radiation approximately 1% UVB/UVA and lower, 2. Lamps with an intermediate proportion of UVB; approximately 1.0-3.0% UVB/UVA, and 3. Lamps with a relatively high proportion of UVB; 3% and above, usually to 5% maximum. In all cases, UVA is defined as the region of 320 nm-400 nm, UVB is defined as the region of 260 nm-320 nm.
In order to alter the UVB proportion of present tanning equipment one must actually replace lamps with others which have a different spectral characteristic. This necessitates the purchase and storage of an additional set of lamps. Another possibility is to alter the design of the tanning unit by installation or alteration of separate filters or reflectors. This latter option is even less desirable than the former in that the total output of the tanning unit will likely be reduced by such modifications. It is also inconvenient to maintain these materials and make the necessary installation.